Hydroxy terminated polybutadiene based polyurethane bound propellant grains

Abstract

Salicylate esters have been found to be suitable blocking agents for polyisocyanates, enabling preparation of hydroxy terminated polybutadiene based polyurethane bound propellant grains having extended pot life. Unblocking occurs readily at normal propellant cure temperatures, allowing normal cure rates.

The subject matter which Applicants regard as their invention is particularly pointed out and distinctly claimed as follows: 
     
       1. A cured hydroxy terminated polybutadiene based polyurethane bound propellant grain wherein the binder and plasticizer comprise the reaction products of a hydroxy terminated polybutadiene and the dissociation products of a compound of the formula: ##STR3## wherein X is an n + m valent organic radical; R is hydrogen or lower alkyl of from 1 to about 10 carbon atoms; R' is lower alkyl of from 1 to about 10 carbon atoms or carbocyclic aryl of from 6 to about 10 carbon atoms; n is on the average at least 1; m is 0 or 1; and n and m must be at least 2. 
     
     
       2. A process for control of the pot life of a curable hydroxy terminated polybutadiene based polyurethane propellant binder which comprises mixing a hydroxy terminated polybutadiene with a compound of the formula: ##STR4## wherein X is an n + m valent organic radical; R is hydrogen or lower alkyl of from 1 to about 10 carbon atoms; R' is lower alkyl of from 6 to about 10 carbon atoms or carbocyclic aryl of from 6 to about 10 carbon atoms; n is on the average at least 1; m is 0 or 1; and n and m must be at least 2; and maintaining the temperature at about 28° C or below.